I. Technical Field
This invention relates to telecommunications, and particularly to multicasting to/with a group of participants.
II. Related Art and Other Considerations
Public safety telecommunications systems have historically existed as dedicated systems which are especially designed for a specific use. As such, typical public safety telecommunications systems have rather peculiar or unique requirements.
Few public safety telecommunications standards currently exist. For example, TErrestrial Trunked RAdio (TETRA) is an open digital trunked radio standard which is defined by the European Telecommunications Standardization Institute (ETSI). Another example is Project 25, a steering committee for selecting voluntary common system standards for digital public safety radio communications. Yet there is no single commonly used standard that dominates the market place. Thus, it is still fair to say that the market for public safety telecommunications is fragmented from a technological and standard point of view. This fragmentation and the relatively small market size of any system have made public safety technology either expensive or shallow in functionality.
Attempts have been made to enable the public safety market to re-use the benefits of (among other technologies) the evolution of the Global System for Mobile Communications (GSM). In addition, the advent of new multi-media enabled networks and new developments in radio access and terminals brings other possibilities. Further, advancements in core networks, radio access and terminals make it continuously easier to offer public safety systems based on main-stream mobile technology.
Push-to-Talk over Cellular (PoC) is a communication service that provides wireless users with a virtually instantaneous method of connecting to other users, with just a push of a button. Push-to-Talk over Cellular (PoC) service is half-duplex, and can be used for person-to-person calls as well as for group communication over cellular networks like GSM, WCDMA or CDMA2000 networks. Push-to-Talk over Cellular (PoC) service thus resembles its predecessor Push-to-Talk (PTT) [also known as “Press-to-Transmit”] in using a momentary button to switch from voice reception mode to transmit mode. As such, Push to Talk over Cellular (PoC) is a walkie-talkie type service that provided over a cellular phone network. A push to talk connection is typically connected virtually instantaneously. A single press reaches an active talk group. Users no longer need to make several calls to coordinate with a group.
There are proprietary implementations of PoC. In addition, the Open Mobile Alliance (OMA) has defined standards for PoC Push-to-Talk over Cellular (PoC). See, for example, Push to Talk over Cellular (PoC)—Architecture, draft version 2.0—March 2007, Open Mobile Alliance, OMA-AD_PoC-V2—0-20070326-D, which is incorporated herein by reference. The OMA PoC specifications set utilize a number of existing specifications from IETF, 3GPP and 3GPP2, including the capabilities of the 3GPP IP Multimedia Subsystem (IMS) and 3GPP2 Multimedia Domain (MMD) to enable IP connectivity and IP based communication between mobile devices.
PoC or a similar IP based push-to-talk based system is proposed to be part of future public safety capabilities. Yet there are problems in making efficient push-to-talk group sessions over radio accesses like GSM/EDGE or WCDMA.
PoC or a similar IP based push-to-talk based system as known today utilizes unicast IP bearers for group communication. A radio bearer is a service provided by Layer 2 for the transfer of user data between a wireless terminal such as a user equipment unit and a radio access network (RAN) [such as a UMTS Terrestrial Radio Access Network]. Use of unicast IP bearers limits the maximum number of PoC Users that can participate in one cell. For example a radio bearer realization over a unicast EDGE (Enhanced Data GSM Environment) radio network may provide ten to twenty simultaneous media bursts comprising voice (voice users in a group) per carrier and cell (assuming that header compression is deployed).
By contrast, public safety telecommunication services on the other hand face challenging requirements with very large PoC Groups that must be supported. A real-life scenario that dramatizes the requirements on PoC Group size occurred in the year 2004 at a fire at the N.P. Johnsen fireworks factory in Denmark. The catastrophe summoned eight hundred responders; approximately half were active. Presently it is not feasible to efficiently support hundreds of simultaneous users (e.g., first responders) using unicast IP bearers in existing radio access technologies.
Some public safety applications have requirements on “unlimited” cell capacity to handle situations at emergency areas where several hundreds of people may need to communicate. To be able to support a large amount of simultaneous users (like first responders in the firework plant fire disaster), some sort of multicasting appears necessary. A multicasting approach referred to as Multimedia Broadcast Multicast Service (MBMS) is being standardized by the Third Generation Partnership Project (3GPP). Multimedia Broadcast Multicast Service (MBMS) is a broadcasting service that can be offered via existing GSM and UMTS cellular networks. The MBMS feature is split into the MBMS Bearer Service and the MBMS User Service. The MBMS Bearer Service includes a Multicast and a Broadcast Mode. The MBMS Bearer Service uses IP Multicast addresses for the IP flows. The MBMS User Service is basically the MBMS Service Layer and offers an Streaming and a Download Delivery Method. 3GPP standards relating to Multimedia Broadcast Multicast Service (MBMS) include the following (all of which are incorporated herein by reference):    3GPP TS 22.146 Multimedia Broadcast/Multicast Service (MBMS); Stage 1    3GPP TS 23.246 Multimedia Broadcast/Multicast Service (MBMS); Architecture and functional description.    3GPP TS 25.346 Introduction of the Multimedia Broadcast/Multicast Service (MBMS) in the Radio Access Network (RAN); Stage 2.    3GPP TS 43.246 Multimedia Broadcast/Multicast Service (MBMS) in the GERAN; Stage 2.    3GPP TR 25.803 S-CCPCH performance for Multimedia Broadcast/Multicast Service (MBMS).    3GPP TS 22.246 Multimedia Broadcast/Multicast Service (MBMS) user services; Stage 1.    3GPP TS 26.346 Multimedia Broadcast/Multicast Service (MBMS); Protocols and codecs.    3GPP TR 26.946 Multimedia Broadcast/Multicast Service (MBMS) user service guidelines.    3GPP TS 33.246 3G Security; Security of Multimedia Broadcast/Multicast Service (MBMS).    3GPP TS 32.273 Telecommunication management; Charging management; Multimedia Broadcast and Multicast Service (MBMS) charging.
However, the pure MBMS concept has been formulated from the perspective of a broadcast type of services, such as television, for example. Broadcast services differ in several respects from multicast services. What is needed, therefore, and an object of the present invention, is a technique for providing multicasting services for terminals with push to talk over cellular type capabilities.